Technical Field
The present invention relates to a control system and a control method for fail safety of motor driven power steering (MDPS), and more particularly to a control system and a control method for fail safety of MDPS by which the type of a fail such as a self-steering or no-steering situation may be accurately detected so that the fail safety of the MDPS may be secured.
Background Art
A motor driven power steering (MDPS) is mounted on vehicles that have recently been released to change a steering force of a steering wheel according to travel speeds of the vehicles.
The MDPS is a vehicle speed adaptive power steering apparatus, and functions to provide an optimum steering feeling to the driver according to the travel speed of the vehicle while an ECU of the MDPS controls a steering angle and a motion of a motor according to the vehicle speed of the vehicle.
As components of the vehicles become electronic, an interest in the fail safety of the vehicles has increased, and accordingly, research and development for satisfying ISO26262 which is an international standard has continued even in the field of the MDPS.
In order to satisfy the international standards and improve the fail safety of the MDPS system, an MDPS fail safety measure has been used.
The existing MDPS fail safety method is realized by a fail safety logic that focuses on breakdowns in which an MDPS fail is expected, such as failure related to a sensor signal mainly input to the MDPS, an ECU internal circuit, and a motor, and a current to the motor of the MDPS is immediately interrupted so that the MDPS operation is stopped without considering an overall state of the vehicle including the MDPS.
However, because a fail safety method for monitoring a function added when a new function of the MDPS is added is developed through a method suitable for an automotive safety integrity level (ASIL) and a fail safety logic is added whenever a function of the MDPS is added, the MDPS fail safety system becomes complex.
As various sensors for realizing a fail safety logic are requested whenever a function of the MDPS is added, manufacturing costs increase.
Accordingly, in order to accurately detect a fail of the MDPS (for example, self-steering or no-steering), the fail needs to be detected in consideration of an overall state of the vehicle without adding a separate sensor.
For reference, the self-steering of the MDPS refers to a phenomenon [ASIL: D (very dangerous)] in which a high torque is generated in a motor for MDPS by a fail of the MDPS in a situation in which an input is not made by the driver (straight motion, circular turning driving, or the like) and thus the vehicle unintentionally deviates from a current travel path.
The no-steering of the MDPS refers to a phenomenon [ASIL: C (dangerous)] in which the steering itself cannot be made as a motor torque for MDPS acts reversely while having the same magnitude as the torque of the driver, in spite of a steering input of the driver due to malfunction of the MDPS.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.